Carbon blacks produced by a furnace process generally have bulk densities ranging from 0.02 to 0.1 gram/cubic centimeter (g/cc) and are generally known as fluffy carbon blacks. Fluffy carbon blacks are generally easy to disperse in liquids, and in some polymeric systems. However, fluffy carbon blacks are generally cohesive and, hence difficult to handle for purposes such as conveying and weighing.
Fluffy carbon blacks are agglomerated by various types of mechanical processes, either in the dry state, or with the aid of a liquid to produce pellets with improved handling characteristics. Common liquid pelletizing agents are oil and water. The process of agglomerating fluffy carbon blacks to form carbon black pellets is generally referred to as pelletizing.
Unfortunately, generally utilized densification or agglomeration (pelletizing) processes have detrimental effects on the dispersion characteristics of the carbon black. Therefore it is recognized in the art that in pelletizing carbon blacks there is a fine balance between acceptable handling characteristics and ease of dispersion.
A process for pelletizing carbon black is disclosed in U.S. Pat. No. 2,065,371 which describes a typical wet pelletization process whereby the fluffy carbon black and a liquid, typically water, are combined and agitated until spherical beads are formed. These beads are then dried to reduce the water content preferably to below 1% to form carbon black pellets.
Prior art patents also disclose the use of binder additives in a wet pelletization process to further improve the pellet handling characteristics.
U.S. Pat. No. 2,850,403 discloses the use of carbohydrates e.g. sugar, molasses, soluble starches, saccharides and lignin derivatives as pellet binders in the range of 0.1% to 0.4%, by weight, based on the dry carbon black. The preferred drying temperature of the wet pellet is disclosed as 150.degree. to 425.degree. C. which together with the residence time is sufficient to carbonize the binder.
U.S. Pat. No. 2,908,586 discloses the use of a rosin emulsion as pellet binders as an alternative to carbohydrates. The preferred level of rosin binder is in the range 0.5% to 2.0%, by weight, based on the dry carbon black.
U.S. Pat. No. 2,639,225 discloses the use of sulphonate and sulphate anionic surfactants as pellet binders at levels of 0.1% to 0.5%, by weight, based on the dry carbon black.
U.S. Pat. No. 3,565,658 discloses the use of a fatty amine ethoxylate non-ionic surfactant where the level of ethoxylation ranges from 2 to 50 moles of ethylene oxide per fatty amine group. The preferred level of surfactant in the pelletizing water is in the range 0.05% to 5%, by weight, based on the dry carbon black.
Similarly, U.S. Pat. No. 3,645,765 discloses the use of a fatty acid or rosin acid ethoxylate, non-ionic surfactant where the level of ethoxylation is 5 to 15 moles ethylene per acid group. The preferred level of addition on the carbon black is in the range 0.1% to 10%, by weight, based on the dry carbon black.
Soviet Union Patent No. 937,492 claims the benefits of using 0.1% to 5%, by weight, based on the dry carbon black, of an aqueous solution of a reaction product generated from urea and an ethoxylated alkylolamide. The preferred level of ethoxylation is 1 to 7 moles of ethylene oxide per alkylolamide molecule.
U.S. Pat. No. 3,844,809 discloses the reduction in pellet dust levels by incorporating 0.4% to 2.5%, by weight, based on the dry carbon black of an aqueous solution containing 0.001% to 0.1%, by weight, of a nonionic surfactant containing randomly repeating poly(ethylene oxide) and poly (dimethyl silicone) groups. Molasses is also included at substantially higher concentration (up to 2%, by weight) as a co-binder and nitric acid (up to 15%, by weight) as an oxidizing source.
The use of carbohydrates, rosin or surface active agents as disclosed in the above patents is focused towards improving pellet handling qualities. The patents do not disclose that the pelletizing treatments affected the performance properties of the carbon black in the final product applications, which are typically rubber orientated.
Japanese Patent No. 1,201,369 discloses the use of a carboxylic acid type amphoteric surfactant in a concentration range 0.001% to 0.1%, by weight, in the pelletizing water to produce carbon black pellets with low adhesion and excellent dispersibility.
U.S. Pat. No. 3,014,810 discloses the benefits of wet pelletizing a range of pigments, including carbon blacks, with a blend of a quaternary ammonium compound and a bis(-2-hydroxyethyl)alkyl amine. Improvements in dispersion rate, viscosity stability and antistatic properties are disclosed for the blend of surface active agents.
Pelletizing with oil, in the presence and absence of water is disclosed in U.S. Pat. No. 2,635,057, U.S. Pat. No. 3,011,902 and U.S. Pat. No. 4,102,967 as beneficial in improving the handling properties of carbon black pellets.
Several patents, including U.S. Pat. No. 2,511,901, U.S. Pat. No. 2,457,962, U.S. Pat. No. 4,440,807, U.S. Pat. No. 4,569,834, U.S. Pat. No. 5,168,012 and Japanese Patent No. 77,130,481 disclose polymers in emulsion, organic solvent solutions and in molten form as means of modifying the pellet properties of carbon black.
U.S. Pat. No. 4,277,288 discloses a fluidised granulation process for producing free-flowing dustless pigment granules in the absence of water. The organic component required to produce a dustless granule consists of two components, 5-20 phr of a non-aqueous granulating aid and a non-ionic surfactant for example sorbitan oleate ethoxylate as a second component. The bulk of the disclosure relates to producing free-flowing organic and inorganic pigments, including carbon black.
U.S. Pat. No. 4,397,652 also discloses a process for producing negligible dust preparations of organic dyes and optical brighteners. The process involves the dry blending, between 30.degree. and 80.degree. C., of the dye, or optical brightener, with 2-10%, by weight, of an adhesive selected from the group consisting of polyhydric alcohol (e.g. sorbitol); manitol; manitose; lactose; hydrated dextrose; neopentyl glycol; and polyethylene glycol with a molar mass above 3,000. Also included in the composition is 1-10% of a dusting aid selected from the group consisting of fatty acid ethanolamide; fatty acid amide; alkyl alcohol; substituted phenol; and polyethylene glycol with a molar mass between 200 and 1000.
U.S. Pat. No. 4,230,501 discloses a pigment concentrate, dispersible in plastics, which is prepared by combining 51-85%, by weight, of a pigment and 14-49%, by weight, of a waxy component. The waxy component is disclosed as being predominantly a natural, petroleum or synthetic wax which has been blended with either polyethylene glycol or a hydrocarbon resin to reduce the melt viscosity and allow better incorporation of the pigment.
Polyethylene glycol is previously known as an additive for direct compounding into thermoplastic compositions.
U.S. Pat. No. 4,013,622 discloses the incorporation of 100 to 600 ppm of polyethylene glycol in the molar mass range of 600 to 20,000 (preferably 1300 to 7500) to reduce the breakdown of polyethylene during blown film operations which is observed as gel formation.
U.S. Pat. No. 4,812,505, U.S. Pat. No. 4,440,671 and U.S. Pat. No. 4,305,849 disclose the use of polyethylene glycols in the molar mass range 1,000 to 20,000 as beneficial for reducing the heat and water-treeing characteristics in polyolefin compositions for electrical insulation. Similarly U.S. Pat. No. 4,612,139 extends this concept of water-tree reduction to include the polyethylene glycol in semiconductive polyolefin compositions containing carbon black.
Similar compositions are claimed in German Patent DE 27 23 488 where polyethylene glycol and other mobile additives are disclosed as being beneficial to reduce the interlaminar adhesion between the insulation layer and outer conductive layer in an electric cable construction.
Polyethylene glycol and branched ethoxylate molecules are disclosed as plasticisers for ethylene-acrylic acid copolymers in U.S. Pat. No. 3,361,702.
United Kingdom Patent GB 975,847 discloses the use of polyethylene glycol, or an aliphatic derivative, in an aqueous solution as a means of producing agglomerates of organic rubber chemicals. A dough is formed as an intermediate which is then converted into pellets and dried at low temperatures.